There was no independent confirmation of the deaths and the Tamil Tigers could not be reached for comment.
Political leader killed
The deaths are the latest in a series of heavy clashes between the two sides in recent days.
On Wednesday Sri Lanka's military said 52 Tamil Tigers and 11 soldiers died, while the Tamil Tigers said 20 soldiers had died and only one of their fighters had been killed.
Last week an air strike killed SP Thamilselvan, the leader of the Tigers' political wing, dashing hopes of ending the two-decade conflict.
The Liberation Tigers of Tamil Eelam (LTTE), or Tamil Tigers, have been fighting for an independent homeland since 1983. The conflict has claimed more than 70,000 lives so far.